Fluid bed reactor systems have been proposed in the past for combustion of various different types of materials. One such fluid bed reactor system is described in U.S. Pat. No. 3,589,313. Foreign objects inerts which are introduced into the system through the material to be combusted collect in the fluid bed. Systems are proposed for removing such foreign objects in U.S. Pat. No. 4,196,676 assigned to the assignee of the present application. The systems disclosed in the latter patent suffer from a number of disadvantages. The particle flow through the removal system would plug up. Also fluid bed particles brought back into the fluid bed would cause mechanical damage and sometimes exit the fluid bed via the opening in the top of the combustion chamber.